The speed and traveled distance of vehicle wheels are commonly sensed by use of an iron rotary device that is fixed to the wheel shaft and that has a cylindrical portion with slots therein. An electromagnetic sensor detects the slots to provide pulses indicating wheel rotation. The electromagnetic sensor is subject to errors caused by magnetic fields such as those near electric utility wires, and magnetic sensors buried in the pavement to detect vehicles. Furthermore, the electromagnetic sensors and iron rotating device with slots, adds weight to the vehicle. An apparatus that could replace presently designed electromagnetic sensors and avoid interference problems, and which could even enable reduction in weight of the rotary device with slots, would be of value.
In accordance with one embodiment of the present invention, an apparatus is provided for sensing rotation of a wheel that can rotate about a wheel axis on a housing, which avoids electromagnetic and magnetic interference problems and which can result in reduced weight. The apparatus includes a frame that is mounted on the housing in place of the electromagnetic sensor, and first and second optical fibers mounted on the frame, with the fibers having forward fiber tips extending primarily parallel to each other. The frame also has a pair of light-reflective surfaces oriented to direct light from a first of the fiber tips to a second of the fiber tips, along a light path that extends through the slots of the optical area of the rotary device. The use of a pair of light-reflective surfaces avoids the need to bend one or both optical fibers about a short radius of curvature, so that large diameter (at least about 0.5 mm) optical fibers can be used for ruggedness and low-cost connections.
The frame is part of a connector, and each optical fiber is part of a short cable that includes a sheath. The sheath is removed at a rear end of the optical cable to leave a bare fiber rear end portion. A metal ferrule has a rear end portion that receives the bare optical fiber rear portion in a close sliding fit therewith, and the ferrule having a front portion that is crimped around the sheath. The front portion is preferably crimped in a circular crimp that leaves a plurality of circular crimp sections that all lie on a circle, with no more than about 40xc2x0 of the crimp circumference not lying on the circle. This results in substantially uniform compressive force applied to the optical fiber to avoid damage to it.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.